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G8MNY > TECH 07.12.24 15:12l 299 Lines 14944 Bytes #999 (0) @ WW
BID : 21037_GB7CIP
Read: GUEST
Subj: Gin polling up large masts
Path: IZ3LSV<ED1ZAC<EA2RCF<SR1BSZ<IW0QNL<JH4XSY<N3HYM<IW2OHX<GB7CIP
Sent: 241203/0810Z @:GB7CIP.#32.GBR.EURO #:21037 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Jun 18)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
A 20M MAST
Over the years I have tried several aerial systems. But settled on a well tried
& tested gin pole system.
The biggest used to date uses 3x 21' (3x 6.5m) aluminium scaffold poles with
reinforced Jaybeam joiners & a 42'(2x 6.5m) steel gin pole. (as we are getting
older a 2nd gin pole is used for putting up the gin!)
.ú:Ý,Pulley
3 tiers of 4 guys @ 90ø ,ú'.;'Ý \
ensures stability. Tight,ú' .', Ý `\
3 Guy ,ú' ,' ,' Ý `\
This design is the Sets,ú' ,' ,' ÝGin `\
mainstay of nearly ,ú' ,' ,' ÝPole `\ Gin
all my contest & ßßßßßßßßßßßßßßßßßßßßßßÝ ` Pull up
/P activity. 20m Mast Ground^ Pivot Rope
Structures higher than 66' (20m) have been attempted, but computer calculations
showed this to would be unstable, and these were borne out in practice when
unstable attempt proved it, i.e. they tend to buckle the mast on lifting with
any head load at all!
METHORD
The mast is always put up with NO aerials first, to make sure all the mast bits
work properly and are in the right place before, the mast is tried loaded. With
the aerial load the mast should be raised slowly and a spotter person used to
sort any snags out. Generally you can tie off the gin up rope at any angle up
to the point of balance, above that someone should slowly pay out the rear 3
mast guys to stop any sudden shock on the mast as it comes vertical & the rear
guys tighten.
If there is to be any length of unsupported mast above the top guy ring, like
in a 17el over 17el on 2m, then an extra top guy is needed during gining up the
mast to stop the top of the mast bending away from the gin (when total collapse
failure is possible!). And this is then untied from the gin & allowed to rap
around the mast when in use.
REINFORCED JOINTS
________________
³o o o o o o³
-----------³~~~~~~~~~~~~~~~~³---------
Mast Poles ³ÍÍÍÍÍÍÍØØÍÍÍÍÍÍͳWebbing
-----------³________________³--------- [³³]
³o o o o o o³ / \
~~~~~~~~~~~~~~~~ WebbingÄ´ ÃÄ
_.-Ä~~~~~~~~Ä-._Webbing \ /
-----------³~~~~~~~~~~~~~~~~³--------- [³³]
³================³
-----------³________________³---------
~Ä-.________.-Ä~
To stop the joiners tearing along the perforated centre line, extra steel
webbings (0.4 x 2 x 25cm) were welded over the weakness both sides. To lighten
it a bit the webbing ends can be cut down.
SLIPPING JOINTS
If the joints stretch and start to slip [³³]
(aerial poles rotate), then put a / \
thin wire (coat hanger) under one of Ä´ .ÃÄ
the sides and clamp up, this will bite \ /\Wire
into the smooth pole and stop slips. [³³]
GUY BEARINGS
Made from either plate or tube collars, resting on a large 2" (50mm) greased
ally washer above the joiners. The top set of guys will rest on an exhaust U
clamp, it also has an enlarged guy spacer is needed to stop the steeper guys
rapping around the pole.
³ ³ Plate ³ ³ Tube ³ ³ Top
==³ ³== Or ,o´³ ³Ão, oÄÄ´³ ³ÃÄÄo
.' ÚÁÄÁ¿ `. .' ³³ ³³ '. .' ³³ ³³ '.
.' ³| |³ '. .' /~ÚÁÄÁ¿~ '. .' /~µ Æ~ '.
³ ³ Washer³| |³ Washer ³ ³\
Exhaust U Clamp
Never use a long unguyed pole (e.g. 10ft) above a guyed joiner, as the wind
loading on your aerial and the pole leverage will try to sheer the joiner in
two! Always use a top guy set and U clamp close to the aerial as possible.
Halyard pullies for wire aerials etc. can be put on the top guy set to, so they
do not rotate with the mast.
CENTRE GROUND POST
(plan views)
Gin ³ ³ Ground Ground Ground
Pole³ ³ Post Post Post
³ ³ (_)___Swivel Mast (_) (_) Swivel clamp
ÄÄÄÄÄÄÄÄ´ÄÃÄÄÅÄÅÄ¿ Clamp ÄÄÄÄÄÄÂÄÂÄÄÅÄÅÄ¿ Mast-( )
ÄÄÄÄÄÄÄÄ´_ÃÄÄÁ=ÁÄÙ ÄÄÄÄÄÄÅÄÅÄÄÁ=ÁÄÙ ÚÅÄÅÄÄÄÄÄÄÄÄÄ
Mast 90øClamp (_)\Tight ÀÁÄÁÄÄÄÄÄÄÄÄÄ
lose Gin pole Clamp 90øclamp Gin Pole
All on the ground Gin up in air Mast up
N.B. the position of the gin 90ø clamp is such, that when put vertical, the gin
and clamp will clear the ground post when the mast is errected.
The gin pole clamp is initially left slightly lose on the mast, so that when
the gin is errected from the side it can rotate on the mast.
GROUND LAYOUT o
All guy ropes use | (5x 5x 80cm)
a safe "clove hitch" | stakes
knot on the bottom of |
the angled stakes. Front Ground | Gin
Stake Post |--goes down---> Back
Once the mast is =======o==========`8<-----12m----->o Stake
up and no further Mast' | -~
adjustment is needed | _-~
the clove hitch can Hinge| 17m
be locked with a. Line| -~
simple over knot. | _-~
o~ Side stakes
A short 1m x 49mm steel ground pole is put it the middle (after making a hole
with the spare 5th stake first) to take all the hinge forces.
ROPES
A full mast rope set of 3 tiers of 4 guys and a gin pole pulley system +2 guys,
takes 1,024' (312m) of rope. Using mainly 8mm polypropylene for strength and
cheapness, caused a storage problem, as the rope is ultra-violet light
sensitive. For speed we do not detach the measured ropes from the guy bearings
for neat rope hank storage, so a single guy tier of 4 ropes with its bearing is
chain-laced together (3x shorter then) to give quick and untangled storage. The
bulky and UV free storage was solved using 2 large dustbins (for 3 mast sets).
One for the 1st mast and Gin pole, and the 2nd for the rest of the masts.
GIN PULL ROPE
ÚÄ¿Thick
³~~³³hook The pull up rope is a
_ððððð Ropes thicker 20mm for hand
Mast _-~_ððððð (clove hitches) hauling and uses a 2:1
top_-~ _-/³ | ³o\ pulley on the gin pole
_- / ³ | ³\/\Strong that hooks on the pole
middle / G³ | ³ \ \Pulley with the mast ropes tied.
/ i³ | ³ \/\ over the steel hook and eye.
/ n³ | ³ \\\Gin Ropes
bottom Side \\\
Guy \\\
The gin pole will need 2 side guys, these need not be at full length 2/3 is OK.
GUYS
The top guy to the gin needs to be low stretch & pre-tightened, so that the top
of the mast ALWAYS bends (curved up) towards the gin pole. This avoids the
unstable failure mode, when the top guy ends up in parallel to the mast and the
very high compression forces on the mast WILL cause a collapse.
.ú:Ý, .ú:Ý,
,ú'.;'Ý \ ,ú'.;'Ý \
,ú' .', Ý `\ ,ú' .', Ý `\
3 Guy ,ú' ,' ,' Ý `\ 3 Guy ,ú' ,' ,' Ý `\
Sets,ú' ,' ,' ÝGin `\ Sets,ú' ,' ,' ÝGin `\
.._,ú' ,' ,' ÝPole `\ ,ú'__...:_ ,' ÝPole `\
~~~ÄÄÄ---...:.____Ý `\ _.:-~~ ~~Ä-..__Ý `\
Good Curved Mast ^ Pivot -~Unstable Mast Fail! ^ Pivot
COAX TIES Beam Boom
With a rotary mast system, reusable ù===ù=ù===ù=Ë=ù===ù===ù===ù
coaxes ties were used on the coax and ~==___º__-Ä~Support
reused to attached it to the mast Coax/ ~~º> coax
above the top bearing. Then 1 or 2 <º loops
lose turns/loops and then attatched Tie.'º'.U clamp
to one of the top bearing guys with .' |º '.bearing
a cable tie threaded through the rope. .' |º '.
(stops it slipping down the rope) .' Coax|º '.
This is then repeated at each lower .' Tie.'²'.joiner'bearing
bearing to take each section of the .' .' |º '. '.
coax's weight, and also keep the coax .' .' |º '. '.
away from the bearings. .' .' |º '. '.
.' .' |º '. '.
TRANSPORT
With the large poles, only roof racks could be used, this caused noticeably top
heavy problems with the vehicles. After some research we solved the problem,
with a designed for a dismantleable pole trailer. The UK law on the length of
long trailers is simple, the trailer other than it's drawbar, must not be
longer than the divisible load.
______
Welded Ý(__[]__)Þ Arm & rubber [³]
Tow .ú'Þ] Wheel frameÝÄÄÄÄÄÄÄÄÞ suspension ³
Hitch úX====X==========================X========X==================X=³
.ú' Þ Þ Ý Þ Þ ³Tail
0<'| Þ Þ Centre pole()XBrace Þ X ³Board
'ú. Þ Þ Ý Þ Þ ³
Welded`úX====X==========================X========X==================X=³
Draw A 'ú.Þ] 2x steel poles (gin) ÝÄÄÄÄÄÄÄÄÞ ³
Frame Ý(__[]__)Þ [³]
Wheel unit
X = scaffold clamps. & mud guard
ù poles
[ forward lights _.-XÄ-.._
] rear light _..-''~ Þ ~`Ä.._
_,.-''~4m 1m Þ [] 3m``Ä-.._
_..-''~ Pole PoleÞ /~~~~\ Pole ~``Ä-.._ o [³]
_ =X====X=========================ÞX³ /~~\ ³X=================X===
(_\____ù____ù_ Þù³³ {} ³³ù
~~~~~~~~~~~~~ \__/Mini
Wheels
We welded up the design, added the trail arm rubber block suspension and axel
and wheels. The upper framework adds essential stiffness for bounce free ride.
It lived up to all expectations, regarding cornering and loadings etc. The only
problem has been the requirement to manually drag the rear and around tight
corners like into the contest site entrance. With experience the wheel unit can
be clamped at a position to set the hitch load to 50kg, dependent on the
planned trailer load. As well as the tail board there are 6 additional running
lights to make the trailer conspicuous as well as being painted in bright
colours. The wiring loom is rapped around the poles and plugs in the fixed
lights etc.
There are 2 shorter bracing poles, that form 2 triangles and are tensioned up
before moving by standing on the long steels & doing up the top swivel camps,
this then forms a very ridged trailer.
The trailer can handle 6 Ally scaffold poles clamped on plus loads more on top.
So it can carry poles for 3 masts using the 2 steels as the shared gin.
The pole trailer is completely dismantled for storage.
AERIALS USED
Mainly concentrating on VHF contests, I have used quite a collection...
BAND
160m 100m random wire to halyard to trees, many other dipoles too!
80m Insulated 66' mast as 1/4 Wave vertical
80m/40m Trap Dipoles, inverted Vs & also plain QRO dipoles
20/15/10m 3el TH33 Mosley beam with QRO traps
6m 3el Coax & Bamboo Quad
6m 5el yagi beam
4m 2x 5el yagi & phasing harness
2m 5el, 7el, 11el small beams, 17el & even 2x 17el 11ft apart
2m 4x 17el yagis Box, 11ft apart stacking frame & power splitter
70cm 9el, 19el, 23el yagis, 88el multibeam
70cm 27el quad loop yagi
23cm 24el, & 65el loop yagi
13cm 40el with tranverter on 10ft extention pole
For 2m we used to use a box of 4x 17el, stack/baying frame & 4 way power
splitter, but due to its weight it could only be put up at 42' and took a good
hour to assemble onto the mast. This gave a theoretical 20dB gain or 40kW ERP!
However the simpler, 2x17el staked at 10'(3m) apart with a coax splitter works
as well in practice at 20m with is wider beam width.
On 4m we stacked 2x5el at 10'(3m) apart as well.
ROTATORS
Generally I use mast ground rotation, avoiding putting the heavy rotators at
the top of the mast. The slightly faster arm strong methods, have been
superseded with bottom of pole rotators, mainly because of access to the mast
under all contest weathers. But I have seen direct drive gearboxes and shaft
into the shack used on simular masts.
_³_³_____________________________
To put a heavy mast on |__________________________ Gin Pole
the rotator, either have ³ ³ ³³
several helpers to lift a /³\ ÝÞ
tiller bar with the guys ³ ³ ³ Þ__Ý Jack
fairly loose. Or use a car ÚÄÁÄÁÄÁÄ¿ ³ ³
jack under the horizontal ³ROTATOR³ ³ ÃÄ¿
gin pole to lift the load Bracing __ÀÄÄÄÄÄÄÄÙ_ ÁÄÄÁÄÙ
while you assemble the Feet U U
rotators clamp on the pole. OR Bolts in
ground
EARTHING ÚÄ¿____³ ³
A when the whole mast is rotated ³X³~~~~³ ³)
I put a flexable 1-2 turn earth ³ ³ ³./
strap from the ground post to the ³ ³ /³\
mast rotator clamp. ³ ³ ³ ³ ³
This earth will take some of the ³ ³ ÚÄÁÄÁÄÁÄ¿
nearby lightening current safely ³ ³ ³ROTATOR³
to earth and not via the shack. ³ ³ ÀÄÄÄÄÄÄÄÙ
N.B. Any direct strike will do ³ ³ U U
lots of damage! ³ ³
WINDAGE
Generally this is not a problem as the gining up process puts much higher loads
on everything than the wind will. Do check guy tensions and knots at least once
a day and after/during any storms. If there are problems and you have the extra
rope it is possible to add an additional guy in situ by lassoing a mast guy set
at ground level and slipping the new guy up the others and stake out windward
etc.
In strong wind raising and lowering, should ONLY be done side on to the wind!
So the only effect it has is to keep one side set of guys tight, and not to
help or hinder the mast raising or lowering.
Y Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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